Ground-source heat pump technology is an effective energy-saving technique form of using shallow geothermal resources. As an important part of the ground-source heat pump, whether a heat transfer pipe is successfully embedded will have a significant impact on the heat transfer efficiency. Using a pile foundation as a carrier for underground pipe embedding to achieve the energy pile that combines the two functions of upper load and heat transfer, has been widely concerned by researchers in recent years. According to different pile foundation construction technologies, a pile embedded ground-source heat pump technology can be mainly divided into two kinds including embedding in a cast-in-place pile and embedding in a prefabricated pipe pile.
The invention patent “PCC (Large Diameter Pipe Pile by using Cast-in-place Concrete) Energy Pile and Manufacturing Method Thereof” (Patent No.: ZL201210298385.5) discloses an embedded form of filling up a heat transfer liquid in a cavity in the PPC pile, and then inserting an opening type or enclosed type heat transfer pipe. The technical method can improve the heat exchange efficiency, but the workload of excavating PCC pile core soil is relatively large.
The invention patent “Prefabricated Hexagonal Energy Pile and Manufacturing Method Thereof” (Application No.: 201310442139.7) discloses a manufacture method of a heat transfer pipe embedded in a pile body during a prefabricating process of a prefabricated pile. The technical solution improves the site construction efficiency, but also increases the prefabricating difficulty.
The invention patent “Heat Exchanging Hollow Pile and Construction Method Thereof” (Application No.: 201510057071.X) discloses a construction method of embedding a ground-source heat pump heat transfer pipe in an opening hollow pile core soil. The technical solution effectively solves the control problem of embedded depth of the heat transfer pipe and the problem that the backfilling compactness of the pile core soil cannot be easily controlled during the backfilling process of the pile core soil so as to affect the heat transfer efficiency. However, the heat transfer pipe may be broken by tension during the embedding process, or the intensity of the heat transfer pipe needs to be increased to ensure that the heat transfer pipe may not be broken by tension, thus increasing the manufacturing cost. Moreover, the method cannot solve the connection processing problem between the vertical heat transfer pipe at the top portion of the pipe pile and the horizontal heat transfer pipe at the upper portion.
To embed the heat transfer pipe in the prefabricated pipe pile usually has the two technical difficulties as follows: (1) there are slurry, soil mass and even sundries in the prefabricated pipe pile, which causes that the heat transfer pipe cannot be effectively disposed to the designed depth and achieve the designed pile embedded form; (2) when the prefabricated pipe pile is connected to a bearing platform or raft in the top portion, the heat transfer pipe is easily damaged; i.e., a connection difficulty between the vertical heat transfer pipe at the top portion of the prefabricated pipe pile and the horizontal heat transfer pipe may be caused while injecting concrete to a certain depth of the pile core and then inserting a steel bar into the pile core to anchor and connect with the upper structure.
All the conventional construction technologies of embedding heat transfer pipes in the prefabricated pipe pile at present face with the two technical difficulties above. Meanwhile, the backfilling compactness of the pile core soil cannot be easily controlled during the backfilling process of the pile core soil, thus affecting the heat transfer efficiency. Therefore, it is particularly necessary to develop a technology of embedding a ground-source heat pump heat transfer pipe in a prefabricated pipe pile, which is rational in technology, economical and effective.